Brakes and Traction Control: Testing and Inspection

Brake System Diagnosis:

BRAKE SYSTEM TESTING
If a road test is needed for diagnosis, test for conventional (non-antilock) braking on a dry, clean, reasonably smooth and level roadway. This test cannot be accurately done if the roadway is wet, greasy, or covered with loose dirt such that all tires do not grip the road equally. Testing also may be adversely affected when the roadway is crowned, throwing the weight of the vehicle toward the wheels on one side, or when the roadway is too rough, making the wheels bounce. Test the brakes at different vehicle speeds, with both light and heavy pedal pressure. Note any unusual noises or handling symptoms. Then test the brakes on a less-than-ideal road surface, such as one of gravel. The ABS mode will engage anytime a wheel locking tendency is detected by the control module. Thus, braking on gravel should cause the ABS to operate, resulting in rapid pulses felt through the brake pedal, and a slight popping or ticking noise heard from the pressure modulator valve assembly. During heavy braking on dry pavement, the tires may make "chirping" sounds intermittently as they approach lock-up. This is less noticeable on wet or icy pavement, or on dirt or gravel roads. Before road testing to diagnose (rather than confirm) ABS related symptoms, refer to the Testing and Inspection.

EXTERNAL CONDITIONS THAT AFFECT BRAKE PERFORMANCE
When road testing the vehicle, be aware of other vehicle systems and conditions which might affect the brake system or generate brake complaints. Be particularly aware of conditions which might cause leading or pulling to one side when the brakes are not applied. Conditions which might cause such, or which might be mistaken for brake problems include:

Tires: Tires having unequal contact and grip on the road will cause unequal braking. Tires must be equally inflated, identical in size, and the tread pattern of right and left tires must be about equal.

Vehicle Loading: A heavily loaded vehicle requires more braking effort. When a vehicle has unequal loading, the most heavily loaded wheels require more braking power than others.

Wheel Alignment: Misalignment of the wheels, particularly excessive camber and caster, will cause the brakes to pull to one side.